When compound pieces of fabric are sewn together, e.g., two different fabric pieces or parts such as a wool garment and a synthetic fiber lining, or two pieces of the same fabric, as in a hem, shirt pocket, etc., a complex stitch, generally referred to as a chain stitch, is used.
Illustratively, in a hemming operation, successive parts to be sewn are placed on a conveyor belt. The edges of the fabric part are trimmed with edge cutting devices, then folded to create the proper size hem. The fabric part then travels through the machine and is stitched. After exiting the machine the trailing chain of thread, which continues to be generated after the part is no longer under the presser foot and needles of the sewing machine, is cut off with a conventional type chain cutter. The completed, sewn, part is then removed from the conveyor and stacked.
In repetitive operations prevalent in industrial usage of sewing machines, difficulty has been encountered in maintaining the continuity of the thread chain so that when the succeeding fabric part is conveyed under the presser foot and the needles, the integrity of the thread chain between successive parts is sustained. With this continuity of the thread chain between parts, the next succeeding part may be stitched properly.
Historically, however, continuity of the chain between successive parts has presented difficulty, especially with certain texture threads. In the interval between stitching of successive parts, there is a tendency for the thread to break, tangle or separate from the needles. The conveyor and sewing machine must then be stopped and the sewing machine rethreaded, a time consuming procedure which disrupts production.